Book/Report

FZJ-2019-01387

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Adsorption und Struktur von N$_{2}$ und CO auf Cu(110) untersucht mittels Streuung thermischer Heliumatome

Goerge, J. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21609

Report No.: Juel-3198

Abstract: The adsorption and the structures of N$_{2}$ and CO adlayers on a Cu(110) single crystal surface have been studied with thermal energy helium scattering. N$_{2}$ molecules form a physisorbed layer which is stable at temperatures up to 29 K. At low coverages N$_{2}$ forms a two-dimensional (2D) lattice gas phase which - due to attractive interactions between the physisorbed molecules - condensates at higher coverages into a 2D solid phase. From the dependence of the condensation coverage upon surface temperature a lateral interaction energy of e$_{l}$ = 5.5 me V is determined. This value is surprisingly small if compared to the lateral interaction energies of rare gas atoms on Cu(110). From adsorption isotherms an isosteric heat of adsorption of the N$_{2}$ monolayer of q$_{1}$ = 88 meV per molecule is obtained. The sticking coefficient of N$_{2}$ on the bare Cu(110)-surface is low (s$_{Cu}$ = 0.32). However, the effective sticking coefficient increases with nitrogen coverage and can be described by a 'modified Kisliuk' model: s$_{eff}$($\Theta$) = s$_{Cu}$(1 - $\Theta$) + S$_{N_2}$$\Theta$G($\Theta$). The occurrence of a highly mobile transient state of N$_{2}$-molecules on the bare Cu(110) is discussed: Upon hitting an 2D N$_{2}$ island these transient molecules are converted into the localized physisorbed state. He-diffraction reveals that at all temperatures below 29 K and exposures from 0.4 to 3 Langmuir the N$_{2}$ molecules form a high-order commensurate (HOC) ([...])-struclure with a nearly hexagonal unit cell. The exact number of N$_{2}$ molecules per unit cell (6, 7, or 8) and the orientation of the molecules cannot be determined from these data alone. At T$_{s}$ < 25 K and exposures above 3 L the moleeules form compressed phases. At T$_{s}$ < 22 K and an exposure of 3.5 L the second N$_{2}$ layer starts to grow which is completed after 5.5L. The energy of the perpendicular vibrational modeof the N$_{2}$ molecules has been determined from TOF data to $\hbar \omega$ = 4.2 meV. A model of the structure of the N$_{2}$ monolayer was calculated assuming semi-empirical pair potentials between the physisorbed N$_{2}$ molecules as wen as between N$_{2}$ and the Cu(110) substrate. With the parameters of the Lennard-Jones potentials estimated from combination rules a holding potential with a wen depth of about 86 meV and a perpendicular [...]

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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